1. Field of the Invention
Embodiments of the present invention relate generally to electrodes for obtaining biosignals from a recording surface, for example a skin of a subject.
2. Description of the Prior Art
When monitoring the vital signs or other physiological parameters of hospitalized patients, sensors are attached on patients' skin or catheters are inserted either into natural openings of the body or catheters are pierced through the skin. The common practice is to connect these sensors with electrically or optically conductive cables to measurement instruments. The instrument may reside either on bedside (e.g. multi-parameter patient monitors in an operating room (OR) or in an intensive care unit (ICU)) or it may be a relatively small box carried by the patient (e.g. ECG telemetry).
Infection control has become a big issue in a hospital environment. The term “disposable” as used herein refers to a single-use sensor which is used once and then disposed. Totally disposable sensors would make infection control easier. They would also streamline the care process by eliminating the need for cleaning the sensors. The use of disposable single-patient-use sensors prevents the spreading of infections and cross contamination inside the hospital. This also improves the care process by saving time and money. There are several disposable sensors available on the market such as a depth-of-anesthesia sensor, SpO2, ECG sensors, etc.
In patient-monitoring devices it is also important to ensure that the sensors are properly attached to the patient and that they provide sufficient signal quality so that the alarms and calculated parameters generated based on the signal are reliable. For this purpose, practically all patient monitors may analyze the signal quality continuously. They may also measure the electrical or optical properties of the sensor contact continuously or intermittently. In the case of insufficient contact or signal quality, the monitor prompts the user to check the particular sensor. The common way to indicate which sensor to check is to refer to it using an established naming system, such as the ‘10-20 electrode system’ in EEG. The message on the monitor screen would be something like ‘Poor ECG electrode contact, check electrode V5’ or ‘Poor EEG electrode contact, check electrode P3’. The electrode naming system is usually printed on the cover of a connector box, in which the individual electrode lead wires are combined into a single multi-wire cable. Obviously, this method of indicating the suspected electrode is complex and difficult to use, especially if the user is not familiar with the naming convention or if the electrodes are at non-standard locations.
Recent technological development has made it possible to build battery-operated sensors, which include means for performing the actual measurement, converting the measured signals into digital format, and transmitting wirelessly the measurement data and/or calculated parameters to a host device. Instead of transmitting the data in real time, it is also possible to store the data in local memory and download the data afterwards. These devices are referred to as wireless sensors. Wireless sensors provide obvious benefits for both caregivers and patients. The so-called ‘cable clutter’ has been recognized as one of the biggest issues in the care process of high-acuity patients. There are a lot of cables in the hospitals that also create issues with infections and the usability. By using wireless sensors one can reduce the amount of cables used in a hospital and improve the usability of the different parameters and the total care process. It is not necessary to remove all the cables, but a significant improvement would be achieved by removing a moderate number of leads or wires. This is because the tendency to tangle increases disproportionally with the number of cables. The patients that would benefit most from the wireless sensors are low-acuity patients. Being not physically tied to the patient monitor with lead wires, they are free to move around, for example, visiting the bathroom without assistance. Also in case of a small patient monitor carried by the patient, wireless sensors offer better reliability and are more comfortable for the patient.
However, in case of wireless, single-use sensors, the problem relating to identifying electrodes is even greater than in established ECG or EEG systems. Firstly, the sensors are often attached in non-standard locations, which makes the naming difficult, especially because there may not be an obvious place to print the electrode placement chart. And secondly, there may be no conventional bedside monitor with a display to indicate the location of the electrode with poor contact.